The present invention relates to a process for obtaining luminescent glass layers. It more particularly applies to the construction of devices equipped with at least one luminescent glass layer, such as certain illumination devices, cathode-ray tubes, image intensifier tubes, X-ray screens and television screens. It also applies to the construction of photoscintillators comprising a scintillating glass layer and a support, said layer being able to emit light by energy absorption and optionally coupled to a photodetector provided with an entrance window.
Photoscintillators of this type can be used more particularly for measuring .alpha.-particle emission rates of liquid acid solutions used in the preparation of actinides and for the continuous control of radioactive effluents from plants for the reprocessing of irradiated fuels from nuclear reactors.
It is frequently necessary to determine the .alpha.-particle emission rate of substances dissolved in a liquid, both in the field of research and in the nuclear industry. In the case where the solution to be studied is corrosive and in circulating, whilst simultaneously having .alpha., .beta. and/or .gamma. radioactivities, the .alpha.-particle detection procedure utilizing a photoscintillator incorporating a scintillating glass layer optically coupled to the entrance window of a photodetector, such as a photomultiplier, has numerous advantages compared with other known .alpha.-particle detection methods, e.g. a good resistance of the glass (having a high SiO.sub.2 content) to organic and inorganic reagents, such as a corrosive nitric acid solutions. This good resistance of the glass makes it possible to use a detection arrangement in which the scintillating glass layer placed against the entrance window of the photomultiplier is in direct contact with the investigated solution. As a result it is possible to illuminate systems provided with a fragile separating window, which is liable to deform. The photoscintillator is then no longer able to see the analysed solution portion under the same solid angle. Due to its robustness, such an arrangement has the advantage of being well adapted to a liquid circulation having flow rate and consequently pressure variations level with the scintillating glass layer.
In the case of a liquid which is at the same time an .alpha., .beta. and/or .gamma. emitter, a good discrimination of the .alpha.-particles compared with the .beta.-particles and/or the .gamma.-photons can be obtained by limiting the liquid portion studied to a layer of limited thickness, namely of a few millimeters, in such a way that few .beta.-particles and/or .gamma.-photons are emitted, whilst giving to the scintillating glass layer thickness a value of the order of the path in the scintillating glass corresponding to the emission energy of the .alpha.-particles to be detected. This path can be less than 20 .mu.m, e.g. approximately 10 to 15 .mu.m.
However, the known processes for producing thin scintillating glass layers do not make it possible to reproducibly obtain such small values for the thickness of such layers. Thus, in particular, the process for melting a thin scintillating glass layer on a support makes it difficult to retain the initial contents of the glass in compounds responsible for the scintillation during the performance of this process and it is virtually impossible to obtain a layer thickness smaller than 300 .mu.m, because by using too little material for producing the thin layer, its final composition (after melting or fusion) differs too greatly from the initial composition for obtaining a scintillating glass. Furthermore, mechanical abrasion of glass makes it possible to reduce the thickness of the latter to 250 .mu.m and the results obtained by continuing this abrasion to about 40 microns, which is far from easy, are of a very arbitrary nature. Moreover, the thin layers obtained in this way are difficult to fix to the entrance window of a photomultiplier.